Communications device and communications method

ABSTRACT

A communications device  100 , which performs data communication, includes an AC cycle sensor  30  which is connected to a power line  106  supplied with an a.c. voltage and generates a synchronous signal SS at timing of an a.c. voltage waveform AC of the power line  106 ; a data communicator  10  for performing data communication; and a communications controller  20  which performs communication of a control signal including information showing at least one of a communications device and a communications standard and controls the data communicator  101 . When the a.c. voltage supplied to the power line  106  is an N-phase and when the cycle of the a.c. voltage waveform is T, data communication to be performed in a communication period subsequent to the period is controlled on the basis of the control signal included in the period of T/2M on condition that M is a natural multiple of N.

BACKGROUND

The present invention relates to a communications device which isconnected to a power line supplied with a predetermined a.c. voltage andperforms data communication over the power line, as well as to acommunications method.

When wired data communication is performed in home, in office, in afactory, or the like, by use of a terminal, such as a computer, wires tobe used as transmission lines, such as cables and connectors, usuallymust be laid at required locations. Hence, various tasks must be carriedout before operation of communications facilities is commenced.

Incidentally, in most cases, commercial power; e.g., an a.c. voltage(for example, 120V-60 Hz in the United States, 100V-50/60 Hz in Japan)is used in the home, the office, a factory, or the like. Accordingly, apower line (a lighting circuit) used for supplying the power has alreadybeen laid at all locations in the house, the office, the factory, andthe like. Consequently, so long as the power line can be utilized fordata communication, a necessity for newly laying a special wire forcommunication purpose is obviated. Specifically, a communicationschannel can be ensured by means of inserting a communications deviceinto the power outlet.

A technique described in, e.g., Patent Document 1, has been known as atechnique for utilizing such a power line for communication. Underpresent circumstances, conditions for utilizing power line communication(e.g., a frequency band) are under consideration in various countries,including Japan.

[Patent Document 1] JP-A-2000-165304

As things stand, specifications have not yet been defined in connectionwith a technique for utilizing a power line for communication such asthat mentioned previously. Specifications of a communications standard,such as a protocol, a modulation system, and a frequency band, which areused for actual communication, vary according to a manufacturer whichdevelops the technique.

When consideration is given to the environment where such acommunications technique is actually used, there is a high probabilitythat a plurality of types of communications standards mixedly exist inthe same location. For instance, on the assumption that users (users ofcommunications devices) reside in multiple housing, such as an apartmenthouse or a condominium, the users residing in the same collectivehousing do not always use communications devices (e.g., modems) of thesame manufacturer. Accordingly, there may arise a case where a pluralityof types of communications devices uniquely manufactured by a pluralityof manufacturers are simultaneously connected to the common power line.

When a plurality of types of communications devices, which differ fromeach other in terms of communications standards, such as a protocol anda modulation system, are connected to the same power line as mentionedabove, a communications device cannot demodulate signals transmittedfrom communications devices of different systems and recognizes thesignals as mere noise. Consequently, despite the fact that the pluralityof types of communications devices use the same frequency band, merepresence of the other communications devices cannot be ascertained. Forthis reason, signals transmitted by communications devices of aplurality of types collide against each other, thereby renderingcommunication impossible. Specifically, difficulty is countered incoexistence of different types of communications devices on the commonpower line.

SUMMARY

The following embodiments has been conceived under the circumstances andaims at providing a communications device and a communications method,which enable control of data communication for avoiding occurrence ofcollision between signals even when a plurality of types ofcommunications devices, which differ from each other in terms ofcommunications standards, are connected to a common transmission line.

First, a communications device that is connected to a power linetransmitting a waveform having characteristics of N-phase and T-cycleand performs communication by way of the power line, the communicationsdevice includes a synchronous generator that generates a synchronoussignal based on the waveform; and a controller that outputs a controlsignal to the power line during a period of T/2M based on thesynchronous signal generated by the synchronous generator, the controlsignal including information for allowing a plurality of communicationsdevices to co-exist on the power line, the M being the N multiplied by anatural number.

By means of this configuration, timing is controlled by use of asynchronous signal generated on the basis of timing of an a.c. waveformof the power line. Hence, even the communications devices of differenttypes can match timing of signal transmission and that of monitoring. Bymeans of setting the period as T/M, an a.c. voltage of N-phase is used.Among a plurality of communications devices whose phases changeaccording to the orientation of a connection between a power plug and areceptacle, control of data communication for avoiding collision betweensignals can be performed.

Second, in the communications device, the M is three.

By means of this configuration, the communications device can cope witha single-phase a.c. voltage and a three-phase a.c. voltage which areadopted in many countries in the world.

Third, in the communications device, the control signal includes arequest for starting communication or communication end information.

By means of this configuration, the communications control section cancontrol data communication by means of solely commencement ofcommunication and end of communication as communication timings of thecontrol signal. Accordingly, processing load imposed on the controlsignal can be lessened.

Fourth, the communications device further includes: a datacommunications section that performs data communication by way of thepower line, wherein the controller controls data communication performedby the data communications section in accordance with the controlsignal.

By means of this configuration, an a.c. voltage of N-phase is used, andamong a plurality of communications devices whose phases vary accordingto the orientation of a connection between a power plug and areceptacle, control of data communication for avoiding collision betweensignals can be performed.

Fifth, in the communications device, the controller controls datacommunication during a communication period sequent to the period inaccordance with the control signal.

By means of this configuration, data communication of the communicationsdevices can be controlled in accordance with information about acoexistence standard included in the control signal.

Sixth, in the communications device, the controller controls datacommunication in a communication period subsequent to the period inaccordance with the control signal received from the othercommunications device.

By means of this configuration, in accordance with a control signaloutput from another communications device, data communication of acommunications device is controlled, thereby enabling data communicationwhich avoids collision between signals.

Seventh, in the communications device, the communication period has alength of the period multiplied by an integer.

By means of this configuration, there is no necessity of changing thecycle of a period. So long as the communications segment is made longer,the processing burden imposed on the control signal can be lessened.

Eighth, in the communications device, the control signal furtherincludes information showing a length of the communication period.

By means of this configuration, the period of the communications segmentcan be adaptively changed during communication, and flexiblecommunication control can be performed.

Ninth, in the communications device, the data communications sectionperforms data communication in each communication period.

By means of this configuration, data communication is performed in eachcommunication period, so that communication can be performed byutilization of a desired data communication band. Thus, frequencyefficiency can be enhanced.

Tenth, in the communications device, the control signal has a pluralityof divided time segments, and specifics of control method are shown by acombination of signals of respective time segments.

By means of this configuration, for instance, the control signal isdivided into K time segments. When binary information is shown in eachtime segment, the control signal can express specifics of control methodof 2^(K) types.

Eleventh, in the communications device, the controller outputs a controlsignal including the same information in each of the plurality ofperiods which are adjacent to each other in terms of time.

By means of this configuration, reliability of coexistence processing ofa control signal can be enhanced.

Twelfth, in the communications device, the controller outputs thecontrol signal when the data communications section does not performsdata communication.

By means of this configuration, the control signal and the data signalare not superimposed on each other in terms of time. Accordingly,leakage of a signal from one band to another band can be prevented, sothat a drop in coverage can be prevented.

Thirteenth, a communications method for a communications device isconnected to a power line transmitting a waveform having characteristicsof N-phase and T-cycle and performs communication by way of the powerline, the method includes: a step of generating a synchronous signalbased on the wave form; and a step of outputting a control signal to thepower line during a period of T/2M based on the synchronous signalgenerated by the synchronous generator, the control signal includinginformation for allowing a plurality of communications devices toco-exist on the power line, the M being the N multiplied by a naturalnumber.

By means of this method, timing is controlled by use of a synchronoussignal generated on the basis of timing of an a.c. waveform of the powerline. Hence, even the communications devices of different types canmatch timing of signal transmission and that of monitoring. By means ofsetting the period as T/M, an a.c. voltage of N-phase is used. There canbe achieved synchronization among a plurality of communications deviceswhose phases vary according to the orientation of a connection between apower plug and a receptacle.

Accordingly, a communications device and a communications method can beprovided, which enable control of data communication for avoidingoccurrence of collision between signals even when a plurality of typesof communications devices, which differ from each other in terms ofcommunications standards, are connected to a common transmission line.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram showing an example generalconfiguration of the communications device according to one embodiment;

FIG. 2 is a functional block diagram showing another example generalconfiguration of the communications device according to the embodiment;

FIG. 3 is a timing chart showing example coexistence processingutilizing an a.c. voltage waveform AC;

FIG. 4 is a block diagram showing the general configuration of acommunications controller according to the embodiment;

FIGS. 5A to 5C are descriptive views showing control timings in theembodiment;

FIG. 6 is a timing chart showing example coexistence processingaccording to the embodiment;

FIG. 7 is a view showing an example data configuration of a controlsignal in the embodiment;

FIG. 8 is a block diagram showing an example configuration of a systemwhere a plurality of communications devices are connected to a commontransmission line;

FIG. 9 is an external perspective view showing the front of thecommunications device according to the embodiment;

FIG. 10 is an external perspective view showing the back of acommunications device according to the embodiment; and

FIG. 11 is a block diagram showing example hardware of a communicationsdevice according to the embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment will be described hereinbelow by reference to FIGS. 1through 11.

First, there will be described a case where communications devices usinga plurality of communications standards are connected to a commontransmission line. FIG. 8 is a block diagram showing an exampleconfiguration of a system where a plurality of communications devicesare connected to a common transmission line. In the embodiment shown inFIG. 8, a plurality of communications devices 100(A1), 100(A2), 100(B1),100(B2), 100(C1), and 100(C2) are connected to a common transmissionline 106. The communications devices 100(A1), 100(A2) performcommunication according to a type-A communications standard; thecommunications devices 100(B1), 100(B2) perform communication inaccordance with a type-B communications standard; and the communicationsdevices 100(C1), 100(C2) perform communication in accordance with atype-C communications standard. The “communications standard” signifiesa protocol used for establishing communication between a transmitter anda receiver. For example, the protocol includes modulation-demodulationschemes such as an OFDM (Orthogonal Frequency Division Multiplexing)scheme and an SS (Spread Spectrum) scheme. Further, the communicationsstandard is a concept encompassing specifications of a symbol rate andthose of a frame format.

Therefore, the communications device 100(A1) and the communicationsdevice 100(A2) are of the same type; the communications device 100(B1)and the communications device 100(B2) are of the same type; and thecommunications device 100(C1) and the communications device 100(C2) areof the same type. However, the communications devices 100(A1, A2), thecommunications devices 100(B1, B2), and the communications devices100(C1, C2) are different from each other in terms of the type. Inreality, a difference among the types signifies a difference incommunications standards, such as a protocol, a data signal modulationsystem, a symbol rate of a data signal, and the like, which are employedin communication.

Power line communication is taken as an example where occurrence of sucha situation is presumed. For instance, collective housing includes aplurality of independent households as users. However, the power lineused as a transmission line is common, and power lines of the respectivehouseholds are electrically connected together. In the meantime, theusers of the respective households do not always use communicationsdevices of the same manufacturers (i.e., the same communicationstandards), and hence there may be a case where the users of therespective households use the communications devices 100 which differfrom each other in terms of type. In short, the communications devices100 may differ from one manufacturer to another manufacturer in terms ofthe communications standard used for communication, such as a protocol,a data signal modulation system, a symbol rate of a data signal, and thelike.

As mentioned above, when the plurality of communications devices 100 ofdifferent types are connected to the common transmission line 106, therespective communications devices 100 cannot demodulate signalstransmitted by the communications devices 100 of different types, andhence cannot even detect presence of the other communications devices100. Consequently, signals transmitted by the plurality ofcommunications devices 100 of different types collide against each otheron the transmission line 106. Since collision between signals disablescommunication, the plurality of communications devices 100 of differenttypes cannot coexist on the transmission line 106, so long as specialcontrol is not carried out.

Accordingly, various types of coexistence standards are mentioned as anexample where the plurality of communications devices 100 of differentcommunications standards coexist in the same transmission line 106.Here, the term “coexistence standard” means a scheme for causing theplurality of communications devices 100 of different communicationsstandards to coexist in the single transmission line 106 such thatcollision of signals is prevented; and signifies that data communicationcomplying with different communications standards are separated fromeach other in terms of a frequency, time, a code, or a combinationthereof, by use of a multidimensional connection system, such asfrequency division, time division, code division, or the like.

In the case of frequency division, when the frequency band used forcommunication ranges from, e.g., 2 to 30 MHz, a communications standardA uses a frequency band from 15 to 30 MHz; and a communications standardB uses a frequency band from 2 to 15 MHz. As a result, thecommunications standard A and the communications standard B can beutilized in the common transmission line.

In the case of the coexistence standard of time division, thecommunications standard A and the communications standard B are switchedat, e.g., predetermined time intervals, the communications standard Aand the communications standard B can coexist on the common transmissionline.

Here, so long as communication is performed by use of only apredetermined frequency band or a time domain according to acommunications standard, collision of signals of differentcommunications standards can be avoided. However, in consideration ofcommunication efficiency, when communication is not performed with aplurality of communications standards, the communications standard bymeans of which communication is being performed preferably uses theentire band.

The embodiment describes a transmission device and a receiving device,which perform coexistence processing among communications devices ofdifferent communications standards by use of a control signal showing acommunications device, a communications method, and the like, and whichenable efficient communication without involvement of collision ofsignals even when communications devices of different communicationsstandards are connected to a common transmission line such as a powerline or the like. The term “control signal” is a signal includinginformation about a coexistence standard for causing a plurality ofcommunications devices of different communications standards to coexistin a power line: specifically, a signal showing control method specificsof coexistence processing, such as communication of which communicationsstandard is performed in what frequency band, communication of whichcommunications standards is performed in what channel (a time domain),what communications standard is prioritized (i.e., given priority), andthe like. As long as the coexistence standard has been set in advanceaccording to a communications device (i.e., the type of a communicationsdevice, such as the name of a manufacturer, a model, and the like), thecontrol signal can also be caused to include only identificationinformation showing that type.

There will now be described a communications device to which thetransmission device and the receiving device of the present embodimentcan be applied. The embodiment provides descriptions by means of taking,as an example communications device, a communications device whichperforms broadband communication (2 to 30 MHz) of the multicarriercommunications standard by using a power line as a transmission line.The communications device of the embodiment is not limited to themulticarrier communications standard, but may also employ a singlecarrier communications standard or a spread spectrum scheme. Thetransmission line used for communication is not limited to the powerline, as well. A transmission line; e.g., a coaxial cable, a phone line,a speaker line, a harness, and the like, may also be used.

FIG. 9 is an external perspective view showing the front of thecommunications device according to the embodiment, and FIG. 10 is anexternal perspective view showing the back of a communications deviceaccording to the embodiment.

As shown in FIGS. 9 and 10, the communications device 100 of theembodiment corresponds to a modem. The communications device 100 has anenclosure 101. As shown in FIG. 9, a display section 105, such as an LED(Light Emitting Diode) or the like, is provided on the front of theenclosure 101. As shown in FIG. 10, a power connector 102, an LAN (LocalArea Network) modulator jack 103 such as RJ45, and a D-sub connector 104are provided on the back of the enclosure 101. As shown in FIG. 10, apower line 106, such as a parallel cable, is connected to the powerconnector 102. An unillustrated LAN cable is connected to the modularjack 103. An unillustrated D-sub cable is connected to the D-subconnector 104. Although the modem shown in FIGS. 9 and 10 are shown asan example communications device, the communications device is notlimited particularly to the modem. The communications device may beelectrical appliance equipped with a modem (e.g., a home electricalproduct such as a TV set).

FIG. 11 is a block diagram showing example hardware of a communicationsdevice according to the embodiment. As shown in FIG. 11, thecommunications device 100 has a circuit module 200 and a switching powersource 300. The switching power source 300 supplies the circuit module200 with +1.2V, +3.3V, and +12V volts. The circuit module 200 isprovided with a main IC (Integrated Circuit) 201, an AFE IC (AnalogFront End IC) 202, a low-pass filter (LPF) 203, a driver IC 205, acoupler 206, a band-pass filter (BPF) 207, an AMP (amplifier) IC 209, anADC (AD converter) IC 210, memory 211, and an Ethernet (RegisteredTrademark) physical layer IC (PHYSIC) 212.

The main IC 201 comprises a CPU (Central Processing Unit) 201 a; aPLC•MAC (Power Line Communication Media Access Control) block 201 b, anda PLC•PHY (Power Line Communication•Physical Layer) block 201 c. The AFEIC 202 comprises a digital-to-analog converter (DAC) 224, ananalog-to-digital converter (ADC) 211, and a variable amplifier (VGA)219. The coupler 206 comprises a coil transformer 206 a and a capacitor206 b.

Moreover, the circuit module 200 is provided with a coexistence IC 251,a coexistence AFE IC 252, an LPF 253, a driver IC 255, a BPF 257, and anAC cycle sensor 30. The coexistence IC 251 is formed from a coexistenceMAC block 251 b and a coexistence PHY block 251 c. The AFE IC 252comprises a DAC 274, an ADC 261, and a VGA 269. The coexistence IC 251processes a control signal pertaining to coexistence processing.Portions or all of the functions of the coexistence IC 251 may beincorporated into the main IC 201. When the main IC 201 plays all of thefunctions of the coexistence IC 251, the coexistence AFF IC 252, the LPF253, the driver IC 255, and the BPF 257 do not need to be provided.

Details of the communications system according to the embodiment will besubsequently described. FIG. 1 is a functional block diagram showing anexample general configuration of the communications device according tothe embodiment.

As shown in FIG. 1, the communications device 100 has a datacommunicator 10 which functions as an example data communicationssection, a communications controller 20 acting as an examplecommunications control section, and the AC cycle sensor 30 acting as anexample synchronous signal generation section.

The data communicator 10 is included in the main IC 201 shown in FIG.11, and is an electrical circuit which performs signal processing,including basic control and modulation-and-demodulation for datacommunication, as in the case of a common modem. Specifically, the datacommunicator 10 modulates a data signal output from the communicationsterminal, such as an unillustrated personal computer, and outputs thethus-modulated data signal as a transmission signal (data). Further, thedata communicator 10 demodulates the data signal input from the powerline 106 as a received signal (data), and outputs the thus-demodulatedsignal to a communications terminal such as a personal computer. Inorder to ascertain whether or not the power line 106 can be used, thedata communicator 10 outputs a predetermined communication requestsignal to the communications controller 20 before communication. Thedata communicator 10 performs data communication at a frequency band andduring a time domain, which are based on a command from thecommunications controller 20.

In synchronism with the timing of a synchronous signal SS output by theAC cycle sensor 30, the communications controller 20 performs controlrequired by the communications devices 100 of the plurality of types tocoexist in the power line 106. Specifically, in accordance with thecommunications request input by the data communicator 10, a certainstation (the communications device 100) performs control for acquiring apriority for usage of the power line 106. In order to conduct anegotiation for acquisition of a priority with another communicationsdevice 100, the communications controller 20 transmits a control signalto the power line 106, and receives the control signal from the powerline 106.

The AC cycle sensor 30 generates a synchronous signal required by thecommunications devices 100 of a plurality of types to perform control atcommon timing. In reality, the waveform of commercial power; i.e., ana.c. voltage waveform AC formed from a sinusoidal waveform 50 Hz or 60Hz, appears in the power line 106 in Japan. Therefore, a zero-crosspoint of an a.c. voltage of voltage waveform is detected, and asynchronous signal SS which takes the timing as a reference isgenerated. The synchronous signal SS shown in FIG. 1 is an example, andcorresponds to a rectangular wave consisting of a plurality of pulsessynchronous with zero-cross points of the a.c. voltage waveform AC. Thea.c. voltage waveform AC is an example of an a.c. waveform of the powerline and may be an a.c. current waveform or an a.c. power waveform.

Switching between receipt of data and transmission of data of the datacommunicator 10 may be controlled by use of an element capable ofcontrolling activation/deactivation of a physical switch. FIG. 2 is afunctional block diagram showing another example general configurationof the communications device according to the embodiment shown in FIG.1.

As shown in FIG. 2, a communications device 100 b has the switch section40 in addition to including the data communicator 10, the communicationscontroller 20, and the AC cycle sensor 30. The switch section 40 is aswitch which is included in the AFE•IC 202 shown in FIG. 11; whichcontrol activation/deactivation of power of the DAC 224; and whichenables and disables passage of a data signal between the datacommunicator 10 and the power line 106. The communications controller 20controls activation/deactivation of the switch section 40 depending onwhether or not the communications device can use the band of the powerline 106 at the current timing. Transmission and receipt of data can beswitched by means of controlling activation and deactivation of anelement connected to a line through which the data signal passes.Switching between transmission of data and receipt of data is not alwayslimited to control of activation/deactivation of power performed by theDAC 224. For instance, another element, such as a driver IC 225 or thelike, may be subjected to activation/deactivation control.Alternatively, an Enable/Disable signal may be transmitted to theelement connected to the line through which the data signal passesrather than activation/deactivation of the element being controlled.

There will now be described example coexistence processing for achievingsynchronization by utilization of the timing of the a.c. voltagewaveform AC as mentioned above. FIG. 3 is a timing chart showing examplecoexistence processing utilizing the a.c. voltage waveform AC.

As shown in FIG. 3, the frequency band of the power line 106 has beendivided into a commercial power band, a control signal band, and a datasignal band. Specifically, the commercial power band is assigned so asto fall within a range of 50 Hz to 2 MHz; the control signal band isassigned so as to fall within a range of 2 MHz to 3 MHz; and the datasignal band is assigned so as to fall within a range of 3 MHz to 30 MHz.A frequency band to be assigned is arbitrary, and can be changed asrequired.

The commercial power range cannot be utilized for communication intendedfor preventing occurrence of interference with commercial power. In thisembodiment, a frequency range of 2 MHz to 30 MHz is further divided intoa control signal band and a data signal band. The frequency rangeutilizing the control signal band and the data signal band does not needto be limited particularly to 2 MHz to 30 MHz unless the frequency rangeoverlaps the commercial power band. Further, the frequency band assignedto the control signal does not need to be limited to 2 MHz to 3 MHz, andthe frequency range assigned to the data signal band does not need to belimited to 3 MHz to 30 MHz.

The control signal band is used specifically for conducting negotiationin order to acquire priorities by means of which the communicationsdevices 100 of the plurality of types use the power line 106 forcommunication. Specifically, the frequency of the control signal shownin FIG. 1 is assigned to the control signal band. The data signal bandis a frequency band specifically designed for use with a signal used inactual data communication. Namely, the frequency of the data signalshown in FIG. 1 is assigned to the data signal band.

Generally, in a range of 2 MHz to 3 MHz, arising noise tends toincrease. In order to achieve high-speed transmission, using the widestpossible frequency band for communication is desirable. However, since alow S/N (signal-to-noise) ratio is achieved in a range of 2 MHz to 3MHz, the fact is that the degree of contribution of this range tohigh-speed transmission is low. Therefore, even when a range of 2 MHz to3 MHz is assigned as a control signal band specifically for conductingnegotiation, a substantial drop hardly arises in transmission rate.

There will now be described an internal functional configuration of thecommunications controller 20 that transmits and receives a controlsignal for negotiation purpose by use of the control signal band asmentioned above. FIG. 4 is a block diagram showing the generalconfiguration of the communications controller according to theembodiment.

As shown in FIG. 4, the communications controller 20 comprises a controlsection 21, a signal generator 22, a digital-to-analog converter 23, alow-pass filter 24, a band-pass filter 25, an AGC circuit 26, ananalog-to-digital converter 27, and an FFT (Fast Fourier Transform)circuit 28.

The control section 21 is a digital circuit which is included in thecoexistence MAC block 251 b of the coexistence IC 251 shown in FIG. 11;and which controls the entirety of the communications controller 20 inaccordance with a communication request input from the data communicator10 or the control signal shown in FIG. 1 and in synchronism with thetiming of the synchronous signal SS input from the AC cycle sensor 30.

The signal generator 22 is included in the coexistence PHY block 251 cof the coexistence IC 251 shown in FIG. 11, and generates a waveformpattern of a signal required to conduct negotiation with anothercommunications device 100 connected to the power line 106, in accordancewith the command from the control section 21. This signal is amulticarrier signal. In the present embodiment, an OFDM signal isgenerated as a control signal. The modulation scheme does not limitedparticularly to OFDM. For instance, W-OFDM (OFDM based on waveletconversion) or SS may also be used.

The digital-to-analog converter 23 is included into the DAC block 274 ofthe coexistence AFE IC 252 shown in FIG. 11, and converts the digitalOFDM signal output from the signal generator 22 into an analog signal.The low-pass filter (LPF) (may also be a band-pass filter) 24 isincluded in the LPF block 253 shown in FIG. 11, and blocks passage ofunwanted frequency components in order to output to the power line 106solely the frequency components of the previously-described controlsignal band.

The band-pass filter (BPF) 25 is included in the BPF block 257 shown inFIG. 11; extracts only frequency components of the control signal bandfrom the signal appearing in the power line 106; and outputs thethus-extracted frequency components to the AGC circuit 26. The AGCcircuit 26 is included in the VGA block 269 of the coexistence AFE IC252 shown in FIG. 11, and amplifies the signal by means of automaticallycontrolling a gain such that an attenuated, input signal achieves aspecified level.

The analog-to-digital converter 27 is included in the ADC block 261 ofthe coexistence AFE IC 252 shown in FIG. 11, and converts the analogsignal input from the AGC circuit 26 into the digital signal. The FFTcircuit 28 is included in the coexistence PHY block 251 c of thecoexistence IC 251 shown in FIG. 11, and subjects the digital signalinput from the analog-to-digital converter 27 to predeterminedhigh-speed Fourier conversion processing, to thus convert themulticarrier signal appearing side by side in the time domain into asignal in the frequency domain. The essential requirement for the FFTcircuit 28 is to perform FFT processing of, e.g., 128 points. Acorrelator may also be used in lieu of the FFT circuit 28.

The control section 21 checks the signal output by the FFT circuit 28,to thus ascertain whether or not the other communications devices 100have transmitted signals as control signals.

FIG. 3 shows an example where coexistence is controlled with apositional relationship between the positions of zero-cross points ofthe a.c. voltage waveform and the control signal. Processing isperformed while a period Tc—a unit used for performing coexistenceprocessing—is taken as a cycle T (60 Hz: 16.67 ms/50 Hz: 20 ms) of thea.c. voltage waveform. When the control signal has come to a positionimmediately after the position of a rising zero-cross point, thecommunications device (or the communications standard) A transmits adata signal in the next period Tc. When the control signal has come to aposition immediately after a falling zero-cross point, thecommunications device (or the communications standard) B transmits thedata signal in the next period Tc.

As mentioned above, since control is carried out in synchronism with thetiming of the synchronous signal generated by the AC cycle sensor 30from the a.c. voltage waveform AC, control timing can be synchronizedwith the other communications device 100 connected to the common powerline 106.

However, there may also arise a case where a lag arises in the timingsof the synchronous signals generated by the plurality of communicationsdevices 100 connected to the common power line 106.

This phenomenon will be described hereinbelow. FIGS. 5A to 5C aredescriptive view showing control timings in the embodiment. FIG. 5A is aview showing a phase lag arising when the power line is supplied with asingle-phase a.c. voltage; FIG. 5B is a view for describing a phase lagarising when the power line is supplied with a three-phase a.c. voltage;and FIG. 5C is a view showing control timings achieved in theembodiment.

The AC cycle sensor 30 shown in FIG. 1 generates a synchronous signal SSat timing of a zero-cross point at which the a.c. voltage in two lines,which constitute the power line 106, change from positive to negative ortiming of a zero-cross point at which the voltage changes from negativeto positive. The communications device 100 equipped with the AC cyclesensor 30 is usually connected to a double-pole power plug or adouble-pole receptacle provided at the single-phase power line 106 viathe power connector 102.

However, the relative orientation between the power plug and thedouble-pole receptacle is not particularly specified. They can beconnected together in an opposite orientation. When the power plug andthe double-pole receptacle are connected in opposite orientation, thepolarity of the a.c. voltage monitored by the AC cycle sensor 30 in thecommunications device 100 is inverted, and the phase becomes reverse. Asshown in FIG. 5A, a phase difference of 180° arises in the waveform ofpower handled in communications devices 100(1), 100(2); namely, thecommunications device 100(1) where the power plug and the double-polereceptacle are connected in a specific orientation (called an “ordinaryorientation” for the sake of convenience), and the communications device100(2) where the power plug and the double-pole receptacle are connectedin a reverse direction. Accordingly, as shown in FIG. 3, when the cycleT of the a.c. voltage waveform is taken as a period Tc, a phasedifference of 180° has arisen between the communications devices 100(1),100(2). When coexistence processing is controlled with the controlsignal being located in the period Tc, control of coexistence processingfails to arise for reasons of the phase difference.

Moreover, when the power line connected to the communications device 100is supplied with the three-phase a.c. voltage, a phase difference of120° arises in a.c. voltages appearing in three lines forming a singlepower line. Consequently, as shown in FIG. 5B, a phase difference of120° arises according to the connected state and orientation ofconnection (polarities) of two lines connected to the AC cycle sensor 30among the three lines.

As mentioned above, when a difference has arisen in timings of theplurality of communications devices 100 at which the synchronous signalSS arises, a difference also arises in the control timings of thecommunications devices 100, so that the communications devices fail tooperate properly.

When the communications devices 100(1) to 100(3), which are connectedwhile being out of phase with each other through 120°, generate thesynchronous signal SS at the zero-cross timings while being connected tothe common power line 106, the synchronous signal SS appears in any ofthe communications devices 100 every 60°.

When the communications devices are connected to a power line suppliedwith an N-phase a.c. voltage, the zero-cross point may appear at timingdetermined by dividing the cycle T of the a.c. voltage waveform by 2N;namely, every T/2N. Consequently, coexistence processing is controlledwhile T/2M (M is a natural multiple of N) is taken as a single unit (theperiod Tc). Thereby, even when there are the communications devices thathave been connected while being out of phase with each other, the timingof the zero-cross point is taken as the synchronous signal SS, and theinfluence of a phase difference can be eliminated.

Namely, when power is the single-phase a.c. voltage, the communicationssegment Tc is set to one-half the cycle T of the a.c. voltage waveformAC. When power is the three-phase a.c. voltage, the communicationssegment Tc is set to one-sixth the cycle T of the a.c. voltage waveformAC. Thus, the influence of the phase difference can be eliminated.

Many of countries in the world adopt the single-phase or three-phasea.c. voltage. Hence, the communications device can cope with both thesingle-phase a.c. voltage and the three-phase a.c. voltage, so long asthe period Tc has been set in advance to T/6. When the communicationsdevice is assumed to be connected to an a.c. voltage having a pluralityof phases, a factor M of T/2M is set in advance to the least commonmultiple of the number of phases, whereby the communications device cancope with the a.c. voltage having a phase of that number. FIG. 5C showsan example where coexistence processing is controlled while the periodTc is set to the length of T/6. When the control signal C istransmitted, the communications controller 20 performs transmission insuch a way that a signal is included in the period Tc.

FIG. 6 is a timing chart showing example coexistence processingaccording to the embodiment. FIG. 6 shows a case where the period Tc isone-sixth the cycle T of the a.c. voltage waveform AC. As shown in FIG.6, in accordance with the control signal included in the period Tc, datacommunication is performed in a communication period subsequent to theperiod.

For instance, when a control signal C1 including information aboutpriority assigned to the communications device (or the communicationsstandard) A has been transmitted to the power line 106, thecommunications controllers 20 of the respective communications devices100 perform coexistence processing such that the communications device(or the communications standard) A performs communication in the nextperiod. When a control signal C2 including information about priorityassigned to the communications device (or the communications standard) Bhas been transmitted to the power line 106, the communicationscontrollers 20 of the respective communications devices 100 performcoexistence processing such that the communications device (or thecommunications standard) B performs communication in the next period.When a control signal C3 including information about priorities assignedto the communications devices (or the communications standards) B, C hasbeen transmitted to the power line 106, the communications controllers20 of the respective communications devices 100 perform coexistenceprocessing such that the communications devices (or the communicationsstandards) B, C perform communication in the next period while dividingthe predetermined frequency range. The control signal C3 may includeinformation used for specifying a frequency range to be used.

The segment of communication processing of a data signal (hereinaftercalled a “communication period”) does not need to be identical with theperiod Tc, but should be a natural multiple of the period. An extent towhich the communication period becomes greater than the period Tc ispreviously set in the communications controller 20. For instance, whenthe communication period is previously set so as to become double theperiod Tc and when a control signal C4 including the information aboutpriority assigned to the communications device (or the communicationsstandard) B has been transmitted to the power line 106, thecommunications controllers 20 of the respective communications devicesperform coexistence processing in such a way that the communicationsdevice (or the communications standard) B performs communication duringa period which is double the period Tc. The duration which is double theperiod Tc is used for data communication.

Information, which defines the length of the communication period ratherthan defining the communication period, may be included in the controlsignal. For instance, when the control signal C4 includes informationspecifying the length of the communication period (which is double theperiod Tc in this case), in addition to including the information aboutthe communications device (or the communications standard) assignedpriority, and has been transmitted, the communications controllers 20 ofthe respective communications devices may perform coexistence processingin such a way that the communications device (or the communicationsstandard) B performs communication during the specified communicationperiod (which is double the period Tc).

As mentioned above, when the communication period is a natural multipleof the period, processing can be performed without a necessity forchanging the cycle (timing) of the period. Further, so long as theduration of the communication period is made longer, processing burdenimposed on the control signal can be lessened.

In addition to including information showing at least one of acommunications device and a communications standard, the control signalmay include information about a request for starting communicationcomplying with the communications device or communications standard orinformation about the end of communication. For instance, a controlsignal C5 shown in FIG. 6 includes information about the start ofcommunication of the communications device (or the communicationsstandard) A, and a control signal C6 shown in FIG. 6 includesinformation about the end of communication of the communications device(or the communications standard) A. When the control signal C5 has beentransmitted, the communications controllers 20 of the respectivecommunications devices perform coexistence processing in such a way thatthe communications device (or the communications standard) A startscommunication. When the control signal C6 has been transmitted, thecommunications controllers 20 of the respective communications devicesperform coexistence processing in such a way that the communicationsdevice (or the communications standard) A ends communication. Thus, datacommunication can be controlled by use of only the start time and theend time of communication as the timings of communication of the controlsignal. Consequently, processing load imposed on the control signal canbe lessened.

There has been described a case where the control signal is output onlyat once during the period C, by reference to FIG. 6. A single controlsignal can also be output consecutively (during the periods Tc which areadjacent to each other in terms of time). By means of thisconfiguration, the reliability of coexistence processing can beenhanced. FIG. 6 has described a case where the control signal and thedata signal are output during a single period Tc. However, the controlsignal and the data signal can also be output in such a way that thesesignals do not overlap each other in terms of time. Thereby, afar-to-near problem of leakage of a signal from one band to another bandcan be prevented, and a drop in coverage can be prevented.

FIG. 7 is a view showing an example data configuration of a controlsignal in the embodiment. As shown in FIG. 7, the control signal C has aplurality of data slots Ts1 to TsK. Information (about control methodspecifics of coexistence processing) included in the control signal isexpressed by means of on/off operations of respective slots. In thiscase, when the number of data slots included in the control signal C isK, operations (information showing control method specifics), whosenumber of types is the K^(th) power of 2, can be expressed by means of acombination of on/off operations of the respective slots. Inconsideration of an error in detection of the AC cycles of thecommunications devices, setting of a guard time Tg is desirable.

According to such a communications device and a communications method ofthe embodiment, timing is controlled by use of the synchronous signalgenerated from timings of the a.c. voltage waveform AC of the powerline. Hence, timings of signal transmission and monitoring ofcommunications devices of different types can be matched to each other.Further, as a result of the period being set to T/2M (M is N multipliedby a natural number), an N-phase a.c. voltage is used, and a pluralityof communications devices of different phases can be synchronized witheach other according to the orientation of connection between the powerplug and the receptacle.

The control signal C shown in FIG. 7 has been described by reference tothe case where one communications device outputs the control signal.However, a plurality of control signals may be output during the periodTc in response to the respective data slots Ts1 to TsK. For instance,data slots may have previously been assigned according to thecommunications standard, and the respective communications devices mayoutput control signals to the data slots complying with thecommunications standards to which the communications devices pertain.Thereby, control method specifics of coexistence processing can also bedetermined in accordance with the values indicated by the data slots Ts1to TsK formed from the plurality of control signals.

For instance, where communications devices of communications standardsA, B, C, D, . . . , are present, the communications devices of thecommunications standards A, B, C, . . . have been set so as to outputcontrol signals in response to the data slots Ts1, Ts2, Ts3, . . . .When “1,” “0,” “0,” . . . are output in response to the control signalscorresponding to the data slots Ts1, Ts2, Ts3, . . . , priority is givento the communications standard A. When “0,” “0,” “1,” . . . are outputin response to the control signals corresponding to the data slots Ts1,Ts2, Ts3, . . . , priority is given to the communications standard C. Atthis time, the control signal of the high-priority communicationsstandard is preferably set at a position as far left as possible in FIG.7 (i.e., the head of the period Tc). As a result, the coexistencestandard of the next period Tc can be determined in an early stage.

Further, a different number of data slots can also have been assignedaccording to the type of communications standard. For instance, when onetype of communications standard adopting frequency division (e.g., anaccess-type communications standard) is present and a plurality of typesof communications standards adopting time division (e.g., acustomer-premise-type communications standard) are present, acommunications device of frequency division is given one data slot, andthe respective time-division communications devices are assigned aplurality of data slots. In connection with frequency division, there isno necessity for causing communications standards adopting frequencydivision to coexist. In the meantime, in connection with time division,there is a necessity for causing a plurality of communications standardsadopting time division to coexist, because the latter case requires agreater amount of information than does the former case. Hence, theperiod Tc can be efficiently used with regard to information about acoexistence standard.

As shown in FIGS. 1 and 2, the previous embodiment has described anexample of communications devices 100, 100 b equipped with the datacommunicators 10. However, adoption of the data communicator 10 is notalways necessary. For instance, a power line communication modem nothaving the function of outputting a control signal is provided with acommunications device (i.e., an adapter which outputs a control signal)including the AC cycle sensor 30 and the communications controller 20,so that the power line and the adapter can be caused to act as thecommunications device 100.

This application is based upon and claims the benefit of priority ofJapanese Patent Application No. 2005-196598 filed on Jul. 5, 2005, thecontents of which are incorporated herein by reference in its entirety.

A communications device and a communications method can be provided,which enable control of data communication for avoiding occurrence ofcollision of signals even when a plurality of types of communicationsdevices, which differ from each other in terms of communicationsstandards, are connected to a common transmission line.

1. A communications device for being connected to a power line toperform communications over the power line, the power line distributingan N-phase alternative voltage comprising N waveforms each having apredetermined waveform cycle having a period T and being offset in phaserelative to each other, the communications device comprising: asynchronous generator that generates a synchronous signal based on thewaveform cycle; and a controller that outputs a control signal to thepower line within a period of T/2M based on the synchronous signalgenerated by the synchronous generator, the control signal includinginformation for allowing a plurality of communications devices toco-exist on the power line, where M=n·N, n being a natural number and Nbeing the number of waveforms of said N-phase alternative voltage,wherein the control signal includes one of (i) a request for startingcommunication and (ii) a communication of end information.
 2. Thecommunications device according to claim 1, further comprising: a datacommunications section that performs data communication by way of thepower line, wherein the controller controls data communication performedby the data communications section in accordance with the controlsignal.
 3. The communications device according to claim 1, wherein thecontrol signal has a plurality of divided time segments, and specificsof a control method are indicated by a combination of signals of therespective time segments.
 4. The communications device according toclaim 1, wherein the controller outputs the control signal to the powerline when the data communications section does not perform datacommunication.
 5. A communications device for being connected to a powerline to perform communications over the power line, the power linedistributing an N-phase alternative voltage comprising N waveforms eachhaving a predetermined waveform cycle having a period T and being offsetin phase relative to each other, the communications device comprising: asynchronous generator that generates a synchronous signal based on thewaveform cycle; and a controller that outputs a control signal to thepower line within a period of T/2M based on the synchronous signalgenerated by the synchronous generator, the control signal includinginformation for allowing a plurality of communications devices toco-exist on the power line, where M=n·N, n being a natural number and Nbeing the number of waveforms of said N-phase alternative voltage; and adata communications section that performs data communication by way ofthe power line, wherein the controller controls data communicationperformed by the data communications section in accordance with thecontrol signal.
 6. The communications device according to claim 5,wherein the controller controls data communication within acommunication period subsequent to the period, in which the controlleroutputs the control signal to the power line, in accordance with thecontrol signal.
 7. The communications device according to claim 5,wherein the controller controls data communication in a communicationperiod subsequent to the period, in which the controller outputs thecontrol signal to the power line, in accordance with a control signalreceived from another communications device.
 8. The communicationsdevice according to claim 7, wherein the communication period has alength equal to a length of the period, in which the controller outputsthe control signal to the power line, multiplied by an integer.
 9. Thecommunications device according to claim 6, wherein the control signalfurther includes information indicating a length of the communicationperiod.
 10. The communications device according to claim 6, wherein thedata communications section performs data communication in eachcommunication period.
 11. The communications device according to claim5, wherein the control signal has a plurality of divided time segments,and specifics of a control method are indicated by a combination ofsignals of the respective time segments.
 12. The communications deviceaccording to claim 5, wherein the controller outputs the control signalto the power line when the data communications section does not performdata communication.
 13. A communications device for being connected to apower line to perform communications over the power line, the power linedistributing an N-phase alternative voltage comprising N waveforms eachhaving a predetermined waveform cycle having a period T and being offsetin phase relative to each other, the communications device comprising: asynchronous generator that generates a synchronous signal based on thewaveform cycle; and a controller that outputs a control signal to thepower line within a period of T/2M based on the synchronous signalgenerated by the synchronous generator, the control signal includinginformation for allowing a plurality of communications devices toco-exist on the power line, where M=n·N, n being a natural number and Nbeing the number of waveforms of said N-phase alternative voltage,wherein the control signal has a plurality of divided time segments, andspecifics of a control method are indicated by a combination of signalsof the respective time segments.
 14. The communications device accordingto claim 13, wherein the controller outputs the control signal to thepower line when the data communications section does not perform datacommunication.
 15. A communications device for being connected to apower line to perform communications over the power line, the power linedistributing an N-phase alternative voltage comprising N waveforms eachhaving a predetermined waveform cycle having a period T and being offsetin phase relative to each other, the communications device comprising: asynchronous generator that generates a synchronous signal based on thewaveform cycle; and a controller that outputs a control signal to thepower line within a period of T/2M based on the synchronous signalgenerated by the synchronous generator, the control signal includinginformation for allowing a plurality of communications devices toco-exist on the power line, where M=n·N, n being a natural number and Nbeing the number of waveforms of said N-phase alternative voltage,wherein the controller outputs the control signal to the power line whenthe data communications section does not performs data communication.16. A communications method for a communications device that isconnected to a power line to perform communication over the power line,the power line distributing an N-phase alternative voltage comprising Nwaveforms each having a predetermined waveform cycle having a period Tand offset in phase relative to each other, the method comprising: (a)generating a synchronous signal based on the waveform cycle; and (b)outputting a control signal to the power line within a period of T/2Mbased on the synchronous signal generated in operation (a), the controlsignal including information for allowing a plurality of communicationsdevices to co-exist on the power line, where M=n·N, n being a naturalnumber and N being the number of waveforms of said N-phase alternativevoltage, wherein the control signal includes one of (i) a request forstarting communication and (ii) a communication of end information. 17.A communications method for a communications device that is connected toa power line to perform communication over the power line, the powerline distributing an N-phase alternative voltage comprising N waveformseach having a predetermined waveform cycle having a period T and beingoffset in phase relative to each other, the method comprising: (a)generating a synchronous signal based on the waveform cycle; (b)outputting a control signal to the power line within a period of T/2Mbased on the synchronous signal generated in operation (a), the controlsignal including information for allowing a plurality of communicationsdevices to co-exist on the power line, where M=n·N, n being a naturalnumber and N being the number of waveforms of said N-phase alternativevoltage; and (c) performing data communication by way of the power line,wherein the data communication is performed in accordance with thecontrol signal.
 18. A communications method for a communications devicethat is connected to a power line to perform communication over thepower line, the power line distributing an N-phase alternative voltagecomprising N waveforms each having a predetermined waveform cycle havinga period T and being offset in phase relative to each other, the methodcomprising: (a) generating a synchronous signal based on the waveformcycle; and (b) outputting a control signal to the power line within aperiod of T/2M based on the synchronous signal generated in operation(a), the control signal including information for allowing a pluralityof communications devices to co-exist on the power line, where M=n·N, nbeing a natural number and N being the number of waveforms of saidN-phase alternative voltage, wherein the control signal has a pluralityof divided time segments, and specifics of a control method areindicated by a combination of signals of the respective time segments.19. A communications method for a communications device that isconnected to a power line to perform communication over the power line,the power line distributing an N-phase alternative voltage comprising Nwaveforms each having a predetermined waveform cycle having a period Tand being offset in phase relative to each other, the method comprising:(a) generating a synchronous signal based on the waveform cycle; and (b)outputting a control signal to the power line within a period of T/2Mbased on the synchronous signal generated in operation (a), the controlsignal including information for allowing a plurality of communicationsdevices to co-exist on the power line, where M=n·N, n being a naturalnumber and N being the number of waveforms of said N-phase alternativevoltage, wherein operation (b) includes outputting the control signal tothe power line when the data communications section does not performsdata communication.